A styrene polymer has a defect of inferior heat resistance when the steric structure has an atactic structure, and has a defect of inferior impact resistance while having excellent heat resistance when the steric structure thereof has a syndiotactic structure. For avoiding the defects accordingly, a styrene copolymer having a syndiotactic structure of a styrene monomer and an olefin, such as ethylene, is proposed (see Patent Documents 1 to 3). However, the catalyst system proposed in Patent Document 3 has low activity at a high temperature that is generally used in production with a plant, and a resulting copolymer is inferior in molding property due to the narrow molecular weight distribution thereof. A block copolymer excellent in mechanical strength is also known (see Patent Document 4), but is inferior in heat resistance due to the styrene part thereof having an atactic structure. Accordingly, associated with enhancement of capabilities of materials, such a styrene copolymer and a production method thereof are demanded that is excellent in heat resistance and impact resistance.
Such a styrene resin composition is known that contains a styrene polymer excellent in heat resistance having a syndiotactic structure having a rubber polymer mixed therein for improving the impact resistance (see Patent Document 5). However, the kind of the usable rubber polymer is limited in consideration of compatibility with the styrene polymer, and when the amount of the rubber polymer for improving the impact resistance is increased, the heat resistance is decreased to make it difficult to attain both the heat resistance and the impact resistance simultaneously. Accordingly, there is a demand of a styrene resin composition having a syndiotactic structure excellent in heat resistance and impact resistance.
By stretching a styrene polymer having high syndiotacticity, a stretched product excellent in mechanical strength, particularly elastic modulus, can be obtained, but the article has a defect in poor ductility. In order to avoid the defect, a styrene derivative is copolymerized therewith to improve the ductility, but such a stretched product of a styrene polymer is demanded that has a syndiotactic structure and is further improved in ductility.    [Patent Document 1] JP-A-3-7705    [Patent Document 2] JP-A-4-130114    [Patent Document 3] WO2006/4068A1    [Patent Document 4] JP-A-2001-354724    [Patent Document 5] JP-A-1-146944